Conventionally known is a spinning forming method of processing and shaping a plate, made of an iron material, an aluminum alloy, or pure titanium, by causing a processing tool to contact the plate while rotating the plate around a predetermined rotational axis.
Even in the case of materials, such as a titanium alloy, which are considered to be difficult to process, the application of the spinning forming method of processing the plate is desired instead of cut processing of forged products in order to reduce a material cost and a processing cost. For example, the titanium alloy, such as Ti-6Al-4V, is high in yield strength and is low in ductility at normal temperature. Therefore, if a conventionally general cold (normal-temperature) spinning forming method is directly applied to the titanium alloy, the material cracks and cannot be shaped successfully. On this account, a hot spinning forming needs to be performed by heating the plate.
The hot spinning forming is disclosed in, for example, PTL 1. According to the configuration in PTL 1, a surface of the plate is heated by a burner, and the plate is then processed.
According to the hot spinning forming using the burner as in PTL 1, the plate is heated extensively. Therefore, even non-shaped portions, such as not-yet-shaped portions, already-shaped portions, and never-shaped portions, of the plate are heated. On this account, there are problems that depending on the material and shape (especially, thickness) of the plate, by stress generated at the time of processing, the not-yet-shaped portion of the plate deforms, so that highly accurate processing cannot be performed, and the already-shaped portion of the plate cracks.
Here, a configuration of PTL 2 is proposed as a spinning forming apparatus that locally heats a position close to a shaping target portion. According to the configuration of PTL 2, a high frequency induction heating coil that is the heater is arranged from between a spatula that is the processing tool and a not-yet-shaped side portion of the plate toward a position where the processing tool and the plate contact each other.